In recent years, people with a normal body weight have become the minority in Germany: 52 percent of Germans are overweight or obese. This development has a dramatic impact, not only on the welfare state in general, but also specifically on medical care. Scientists from the Cluster of Excellence "Inflammation at Interfaces", led by Professor Matthias Laudes, have proven that inflammatory changes in certain regions of the brain are associated with an increase in body weight. The data suggests that through the "gut-brain axis", poor nutrition triggers a change in the intestinal microbiome, which causes inflammatory changes in the brain regions that control appetite and regulate the feeling of being full - leading to long-term weight gain. The study has just been published in the international journal Diabetes.

In the brain, the so-called hypothalamus - an area in the diencephalon (interbrain) with a diameter of approximately three millimeters - controls the appetite and the feeling of being full, amongst other things. To date, very few studies have been able to demonstrate that inflammatory changes in this area have a significant influence on the weight of a person’s body. In the current study, the researchers compared the brain areas of overweight and normal weight persons, using magnetic resonance tomography. In obese people, they found inflammatory activities in the hypothalamus region. "However, we can’t yet say with certainty what comes first," explained first author Carina Kreutzer, a member of the Cluster of Excellence "Inflammation at Interfaces", and of the Department of Internal Medicine I at the University Medical Center Schleswig-Holstein. "So whether obesity causes inflammation in the hypothalamus, or whether the inflammatory processes cause obesity." Of course, both nutrition as well as genetic factors also play a considerable role.

The team, under the direction of Professor Matthias Laudes of the Faculty of Medicine at Kiel University and the Department of Internal Medicine I at the University Medical Center Schleswig-Holstein, also examined the intestinal microbiome, i.e. the bacterial composition of the digestive tract. The researchers were able to identify two bacteria that potentially have a protective influence. If a person eats a well-balanced diet, not too rich in fat, then many of these bacteria live in the gut, and the inflammation values in the body are low. "Conversely, a high-fat diet can reduce the number of bacteria within a relatively short period of time, causing, amongst other things, increased inflammation levels in the brain," said the diabetologist Laudes. "In our study, we see a direct link between brain inflammation and specific changes in the intestinal microbiome. Our data suggests that through the "gut-brain axis", poor nutrition triggers a change in the intestinal microbiome, which causes inflammatory changes in the brain regions that control appetite and satiety regulation - leading to long-term weight gain.“

Tissue sections show that in obese people (bottom row) significantly denser tissue is present in the hypothalamus. This thickening is an indicator of inflammatory processes. In individuals who have a normal weight (top row) the thickening is significantly less.

Pictures: Philip Rosenstiel

A magnetic resonance tomographic recording shows the cross-section of a human brain. The hypothalamus (MBH), measuring approximately three millimeters, is recognizable in the center.